1. Field of the Invention
The present invention relates to a brushless electric machine having a plurality of flux loops and, more particularly, to a brushless electric machine including a stator having a plurality of magnetically isolated stator elements for interacting with a plurality of rotor elements having permanent magnets.
2. Description of the Related Art
Most early designs of electric machines utilized an end of a ferromagnetic member to create torque, which merely utilized half potential of electric machines. Current rotary electric machines utilize two ends of a winding to provide a larger effective air-gap surface area between the rotor and the stator for the purposes of creating the torque of the electric machines. However, adjacent magnetic poles adversely affect concentration of flux in the structure of conventional general-purpose electric machines and result in undesired transformer interference effect.
U.S. Pat. No. 6,791,222 to Maslov et al. discloses a rotary electric machine utilizing two ends of a winding to increase the air-gap surface area between the rotor and the stator. The transformer interference effect resulting from the flux between adjacent windings is eliminated by isolating pole pairs from one another. The stator of such a D.C. electric machine includes a plurality of ferromagnetically isolated electromagnets. The axially aligned rotor magnets and the stator poles provide concentrated flux that can be focused on a relatively large surface to produce high torque. Furthermore, a sensor detects relative position between the rotor and the stator for optimally controlling winding current on the electromagnets at different times, thereby allowing smooth operation of the electric machine.
In U.S. Pat. No. 6,891,306 Maslov et al. improves the structure of the above-mentioned electric machine to obtain larger overall effective air-gap surface area. By increasing the surface areas of the stator poles and the rotor magnets and through improved flux distribution resulting from concentration of flux, larger flux distribution is provided. Thus, the electric machine provides larger continuous flux-producing paths between the rotor elements and stator elements. By increasing the surface area between the rotor poles and the corresponding stator poles extending through a plurality of air-gaps, flux can be focused on a relative larger surface to further increase the torque of the electric machine. In the two electric machines mentioned above, the interaction of the electromagnetic forces is in the axial direction such that axial imbalance will result in adverse affect to the electric machines. In practice, the spatial arrangement of the windings must be considered before operation to achieve geometrically radial balance in space, which, in operation, is achieved by simultaneously controlling the associated windings. In this case, operation of all of the associated windings must be stopped to maintain the geometric balance even though only one of the associated windings malfunctions. This not only reduces flexible operating characteristics of the electric machines but also increases the torque ripple.
The present invention is intended to reduce adverse affects to the electric machine when axial imbalance occurs and to enhance the flux distribution of the poles such that the flux can be focused on a larger pole face, thereby enhancing efficiency and output of the electric machine while lowering torque pulsation and maintaining safe, flexible operating characteristics.